Examples of liquid junctions for reference electrodes are shown in FIG. 1 and FIG. 2. In these examples, a liquid junction of plate or rod shape consists of Teflon and is fixed to a supporter 3 with a rubber packing or a binder 2 (FIG. 1), or a liquid junction 1' is prepared, after molding a polymer of tetrafluoroethylene mixed with potassium chloride under a pressure and sintering it, by scraping a portion of the molded product into a thinner layer to reduce its electrical resistance (FIG. 2).
However, in the case of the electrode of FIG. 1, sometimes problems arise with respect to the chemical stability of the rubber packing or the binder to the solution which is to have its ionic concentration measured, and moreover problems arise regarding the thermal stability of the rubber packing or the binder. In the case of the electrode of FIG. 2, it is rather difficult to make a portion of the molded polymer into the thinner layer and moreover, there is a possibility of introducing error into the measurement of the ionic concentration of a solution by the appearance of an electric potential difference between an internal liquor and the solution in the region of a thicker portion 3' in FIG. 2, since the absorption of the solution to be measured by the thicker portion 3' cannot necessarily be neglected under all conditions.